Our invention relates generally to apparatus having a data transducer for reading and/or writing of data on disklike record media such as magnetic disk and, particularly, those of the "fixed" or hard disk variety. More particularly, our invention has to do with an improved system for controlling the position of the transducer with respect to a multiplicity of concentric data tracks on the disk.
It has been known to employ a two-phase encoder or optoelectronic transducer for detecting the positional relationship between the data transducer or head and the data tracks on the magnetic disk. The provision of the two-phase output requires two light sources and two photodetectors arranged with a phase difference of 90 degrees on both sides of a multiple apertured rotary disk or scale. This conventional encoder configuration is not so simple as can be desired.
We cite U.S. Pat. No. 4,396,959 to Harrison et al. as the prior art comparable to our invention. It describes and claims a transducer position control system in an environment of an eight inch diameter, hard magnetic disk memory system. A key feature of this known transducer position control system is what may be described as a polyphase encoder or electro-optical transducer. It comprises a light source such as a controlled current light emitting diode, a scale rotatable with the head structure and having a series of equally closely spaced microscopic radial lines, and an integrated circuit photosensitive array, which in combination produce a polyphase sawtooth servo waveform. The photosensitive array must provide five outputs, four of these being quadrature track position signals and the fifth being a signal indicative of the location of the head at track zero. We object, here again, to the complex configuration of the polyphase encoder.